Conductive polymer composition

ABSTRACT

Electrical conductivity of a polymeric material is increased by the addition of a compound represented by the formula 
     
         [CF.sub.3 --(R).sub.0-2 --SO.sub.3 ].sub.x M 
    
     wherein M is a metal selected from Groups IB, IIB and VIII of the Periodic Table, x is the valence of M, and each R, if present, is selected independently from CH 2  and CF 2 . Examples of M include zinc, cadmium, mercury, copper, nickel and silver. The presently preferred material, for availability and effectiveness, is zinc trifluoromethanesulfonate, in which M is zinc and there are no R groups present.

This invention relates to electrically conductive polymers. It furtherrelates to a method for preparing an electrically conductivepoly(arylene sulfide) film.

Commercial use for electrically-conductive polymers and polymercompounds are increasing. Compositions having moderate conductivity(10⁻¹² to 10⁻⁸ ohm⁻¹ cm⁻¹) are used where electrostatic discharge isimportant, such as in the computer and electronics industry.Semiconductive polymers (10⁻⁷ to 10° ohm⁻ cm⁻¹) are being developed foruse in p-n junction devices, such as solar cells.

It is known that some thermoplastic polymers can be made electricallyconductive by doping with a chemical agent. For example, electricalconductivity can be imparted to poly(phenylene sulfide) by doping thepolymer with arsenic pentafluoride. Toxicity and stability would beconsiderations in the development of such a material, but the experimentsuggests the potential for making this commercially-important materialelectrically conductive.

It is therefore an object of the invention to provide anelectrically-conductive polymer. It is a further object to provide anarticle of manufacture containing an electrically conductive polymer. Ina specific embodiment, it is an object of the invention to providesemiconductive or conductive poly(arylene sulfide).

BRIEF DESCRIPTION OF THE INVENTION

According to the invention, conductivity of a polymeric material isincreased by the addition of a compound represented by the formula:

    [CF.sub.3 --(R).sub.0-2 --SO.sub.3 ].sub.x M

In one embodiment, a poly(arylene sulfide) is made more electricallyconductive by the addition of zinc trifluoromethanesulfonate.

DETAILED DESCRIPTION OF THE INVENTION

Any polymeric material which is capable of electrical conductivity withthe addition of a doping agent is suitable for the invention compositionand method. Such polymeric materials include thermoplastics such aspolyethylene, polypropylene and copolymers incorporating these. Other,highly suitable polymers include poly(arylene sulfide)s andpolysulfones. In general, such polymers include aromatic moieties havingsulfide (--S--), ketone (CO) and/or sulfone (SO₂) linkages. Examples ofsuch polymers include poly(phenylene sulfide), which can be prepared bythe methods of U.S. Pat. Nos. 3,354,129 and 3,919,177, poly(arylenesulfide/sulfone), which can be produced by reacting sodium sulfide andbis(p-chlorophenyl)sulfone, and ploy(benzophenone sulfide) prepared byreacting dichlorobenzophenone and sodium sulfide as described inChemical Abstracts, Vol. 97, 216826Z.

The salt which is added to the polymeric material for impartingelectrical conductivity can be represented by the formula

    [CF.sub.3 --(R).sub.0-2 --SO.sub.3 ].sub.x M

wherein M is a metal selected from Groups 1B, 11B and VIII of thePeriodic Table, x is the valence of M, and each R, if present, isselected independently from CH₂ and CF₂. Examples of M include zinc,cadmium, mercury, copper, nickel and silver. The presently preferredmaterial, for availability and effectiveness, is zinctrifluoromethanesulfonate, in which M is zinc and there are no R groupspresent.

Any method of incorporating the salt into the polymeric material issuitable as long as good dispersion is obtained. It is suitable, forexample, to intimately mix by dry grinding the polymer in solid formwith the salt in pure, solid form. The resulting mixture can then bemolded by extrusion or compression means into electrically conductiveobjects, often in the form of film or thin sheet.

Poly(phenylene sulfide) film produced from compression molding is tanand opaque. Thermal analysis data suggest that the film is notcrystallized to any significant extent. Representative thermalproperties of a test sample included Tg=87C, Tc=126C, and Tm=275C.

The salt is incorporated into the polymer in an amount effective forincreasing the electrical conductivity of the polymer. The amount willvary depending upon the particular polymer and salt used and theelectrical conductivity desired. Levels of the salt of at least about 3weight percent, preferably at least about 6 weight percent, aresuitable. In general, the salt will make up from about 3 weight percentto about 12 weight percent, preferably about 6 weight percent to about10 weight percent of the polymer and salt mixture.

It has been found that the purity of the chemical agent affects thelevel of imparted conductivity. It is therefore desirable to obtain thesalt from a source which provides consistently pure reagents.

A molded article obtained from the polymer-salt mixture can be used fora variety of commercial purposes. Polymers having moderate conductivity(10-¹² to 10-⁸ ohm⁻¹ cm⁻¹) can be used in p-n junction devices, such assolar cells.

EXAMPLE I

A typical procedure is described for preparing films and evaluatingadditives. A mixture of 97 parts by weight poly(phenylene sulfide), thesample of which was an uncured PPS from Phillips Petroleum Companyhaving a melt flow 20-65 g/10 min at 316° C. at 5 Kg load according tomodified ASTM D-1238, and 3 parts by weight zinctrifluoromethanesulfonate (Alpha Products) were intimately mixed bygrinding in a mortar and pestle. The resulting powdered mixture was thendried in a vacuum oven at 110° C. overnight. The dried powder was evenlyspread into a thin 4 inch×4 inch picture frame mold and compressionmolded between two pieces of aluminum foil at 315° C. for 6 to 10minutes at 35,000 psi ram force. The frame, foil and contents wereremoved hot and allowed to cool slowly to room temperature to give atransparent or opaque film 4 inches×4 inches×0.063 centimeters. Filmsamples were tested for conductivity by placing a 0.5 inch wide strip offilm lengthwise across two strip terminals 0.5 inch apart and connectingthem to a 45-volt cell battery. The current across the film sample wasdetermined with a Keithley Electrometer, Model 610C. The voltage wasalso determined. From the measurements obtained, conductivity wascalculated using the formulas ##EQU1## where σ_(V) =conductance inohms⁻¹ cm⁻¹

ρ_(s) =surface resistivity in ohms/square

t=film thickness, cm.,

and

    ρ.sub.s =R.W/l

where ##EQU2## W=film width in cm. l=film length in cm.

Based on the described procedure, the effect of zinctrifluoromethanesulfonate on the conductance of PPS film was determined.These results are listed in TABLE I where it can be shown that goodconductance is obtained when about 6 to 10 weight percent of the zincsalt is present. The results show that at 10 weight percent (10 partszinc salt, 90 parts PPS) the zinc salt provides more PPS conductancethan the corresponding silver salt (Run 3) or zinc powder (Run 2).Compositions having 10⁷ to 10⁰ ohm⁻¹ cm⁻¹ conductivity were consideredsemiconductive and useful in areas such as solar cells. The data alsoshow that purity of the zinc trifluoromethanesulfonate additive to beimportant because film conductivities varied with different shipmens orlots (compare runs 5 to 7).

                  TABLE I                                                         ______________________________________                                        Effect of Zinc Trifluoromethanesulfonate                                      on the Conductivity of PPS.sup.(a)                                                                     Conductivity,                                        Additive                 ohm.sup.-1 cm.sup.-1                                 ______________________________________                                        1.  no additive              5.9 × 10.sup.-12                           2.  10 wt. % zinc powder.sup.(b,f)                                                                         1.1 × 10.sup.-12                           3.  10 wt. % silver trifluoromethanesulfonate.sup.(c)                                                      1.2 × 10.sup.-10                           4.  3 wt. % zinc trifluoromethanesulfonate.sup.(c)                                                         3.5 × 10.sup.-11                           5.  6 wt. % zinc trifluoromethanesulfonate.sup.(c)                                                         1.8 × 10.sup.-7                            6.  6 wt. % zinc trifluoromethanesulfonate.sup.(d)                                                         4.7 × 10.sup.-11                           7.  8 wt. % zinc trifluoromethanesulfonate.sup.(e)                                                         3.9 × 10.sup.-11                           8.  10 wt. % zinc trifluoromethanesulfonate.sup.(e)                                                          2 × 10.sup.-7                            ______________________________________                                         .sup.(a) Poly(phenylene sulfide), Phillips Petroleum Co.                      .sup.(b) Zinc dust from Mallinckrodt Chemical Co.                             .sup.(c) Available from Alpha Products.                                       .sup.(d) A mixture of zinc salt from two lots.                                .sup.(e) Zinc salt from a second lot.                                         .sup.(f) Dry blended with PPS, extruded at 316° C., ground in Wile     mill and compression molded to film.                                     

I claim:
 1. A composition comprising a poly(arylene sulfide) and fromabout 3 weight percent to about 12 weight percent, based on the weightof the composition, of a solid represented by the formula

    [CF.sub.3 --(R).sub.0-2 --SO.sub.3 ].sub.x M

wherein M is selected from the metals of Groups IB, IIB and VIII of thePeriodic Table, x is the valence of M and R is selected from CH₂ andCF₂.
 2. The composition of claim 1 in which M is a metal of Group IIB.3. The composition of claim 2 in which M is zinc.
 4. The composition ofclaim 3 in which the poly(arylene sulfide) comprises poly(phenylenesulfide).
 5. The composition of claim 4 in which the poly(arylenesulfide) comprises at least two aromatic moieties joined by sulfidelinkages.
 6. A composition comprising a poly(arylene sulfide) and anamount of a solid represented by the formula

    [CF.sub.3 --(R).sub.0-2 --SO.sub.3 ].sub.x M

effective for increasing the electrical conductivity of the poly(arylenesulfide), wherein M is selected from the metals of Groups IB, IIB andVIII of the Periodic Table, x is the valence of M and R is selected fromCH₂ and CF₂.
 7. The composition of claim 6 in which M is zinc.
 8. Thecomposition of claim 6 in which the poly(arylene sulfide) comprisespoly(phenylene sulfide).
 9. The composition of claim 7 in which the zinccompound is present in an amount of at least about 3 weight percent,based on the weight of the composition.
 10. The composition of claim 9in which the zinc compound is present in an amount of about 6 weightpercent to about 12 weight percent.
 11. A method for increasing theconductivity of a poly(arylene sulfide) comprising dispersing in thepoly(arylene sulfide) an amount of a solid represented by the formula

    [CF.sub.3 --(R).sub.0-2 --SO.sub.3 ].sub.x M

effective for increasing the electrical conductivity of the poly(arylenesulfide), wherein M is selected from metals of Groups IB, IIB and VIIIof the Periodic Table, x is the valence of M, and each R is selectedindependently from CH₂ and CF₂.
 12. The method of claim 11 in which M iszinc.
 13. The method of claim 11 in which the dispersed compound ispresent in an amount of at least about 3 weight percent, based on theweight of the dispersed compound and the polymeric material.
 14. A filmhaving an electrical conductivity of at least about 10⁻⁷ ohm⁻¹ cm⁻¹produced from the composition of claim
 1. 15. The composition of claim10 in which the zinc compound is zinc trifluoromethanesulfonate.
 16. Thecomposition of claim 8 in which the zinc compound is zinctrifluoromethanesulfonate.
 17. The method of claim 11 in which the solidrepresented by the formula [CF₃ --(R)₀₋₂ --SO₃ ]_(x) M is dispersed inthe poly(arylene sulfide) by grinding into an intimate mixture.
 18. Thecomposition of claim 1 which is a solid powdered mixture.
 19. A filmproduced from the composition of claim 6.